Polyacrylamide gel: an efficient tool for easy synthesis of multicomponent oxide precursors of ceramics and glasses

The combination of citrate complexation in aqueous chemistry with the steric entrapment effect of an auxiliary organic gel affords the possibility of easy and rapid synthesis of high quality multicomponent oxide powders. Stable solutions of strongly chelated cations are obtained by controlling the amount of ligand and the pH. These solutions are then easily gelled by in situ formation of polyacrylamide gel. This hydrous gel is directly decomposed by thermal treatment, resulting in fine and nanoscale powders. The polyacrylamide gel makes the citrate process easier and more rapid. The chemical homogeneity of the powders, usually high for the citrate process, may be improved by the steric effect of the organic gel. The process, routinely used for hundreds of preparations is illustrated by the synthesis of four compounds as examples. Nearly single-phase calcium hexaaluminate CaAl₁₂O₁₉ is obtained after heat treatment at 1100°C for 1 h. Pure lanthanum manganite La_0.8Sr_0.2MnO₃ and barium zirconate BaZrO₃ are formed at 650 and 1000°C, respectively. The synthesis of anorthite CaAl₂Si₂O₈ is an example of the use of this process for silicates or aluminosilicates in aqueous chemistry without citrate chelation. The amorphous precursor crystallises at 1000°C into hexagonal anorthite before transforming into the stable triclinic form. The steric entrapment effect of the polyacrylamide gel is advantageous for aqueous chemical processes, and in the same way, the same concept may be used for other organic gels in organic media.